Chemical senses Flashcards
why do we have senses
to depict the world around us
detect good and bad stimuli
evoke positive and negative responses to ensure our survival
what is the olfactory system
the system which determines our sense of smell
what is odour identification dependent on
the oderant - molecules the olfactory system can specifically recognise
single receptor tuned to small subset of orderants
the concentration - must be large enough in air to evoke a response
define transduction
neural activity that occurs when odour molecules activate receptors in the nose/mouth
what is the detection threshold for vanillin
0.000035 ppm
strong in small concentrations
wat is the detection threshold for methanol (ie antifreeze)
141 ppm
strong in high concentrations
define ‘Just Noticeable Difference’ (JND)
% concentration in air that needs to be changed by in order to recognise the odourant
can be as little as 5%
describe how no visual information can impact on the identification of odours
found to have generally poorer perfomance w/o visual info
identification seems to rely heavily on contextual cues ie smell flowers when in a garden
how does age influence odour identification
doty et al 1984
70yrs - drop off point in ability to smell odours
generally more likely in males than females
what is used to test smell identification abilities?
university of pennsylvania smell identification test (UPSIT)
how can smoking influence odour identification
frye et al 1990
smoking can be detrimental
strong association between years smoked and ability to detect different odours
how many types of olfactory receptors are there
350 types
10,000-20,000 of each type
how is the olfactory system laid out
olfactory bulb located above nasal passage
has cilia of olfactory receptor neurons which go into nasal passage
nasal passage lined with mucus to pick up odour molecules
what is the function on olfactory receptors
detect specific subtypes of odours
what are GPCRs
G protein coupled receptors - specific class of ORN predominant in the function of taste and smell
how do odours and receptors interact?
odour molecules dissolve into nasal mucosa
make contact with receptor
calcium and sodium enter receptor cells via ion channels
summation at axon hillock - determines ap to brain if threshold reached
signal sent to gloeruli in olfactory bulb which sends to higher cortical areas
describe malnic et al 1999
receptors and oderants are specific in mice octanoic acid and noanoic acid activate receptors 1,18,19,41,46 and 51 BUT octanoic also 79 and 83 noanoic also 83 and 86 - specific amount for a specific pattern
describe glomeruli in olfactory bulb
fletcher et al 1999
diff odours produce specific patterns of activation in glomeruli subsets
receptors of one type conerge at same point on glomeruli
how are odours synthesised in the cortex
olfactory mucosa > olfactory bulb piriform cortex orbitofrontal cortex
olfactory bulb entorhinal cortex
entorhinal cortex orbitofrontal cortex/hippocampus
olfactory bulb amygydala hypothallamus/piriform cortex/orbitofrontal cortex
orbitofrontal cortex>hypothallamus
COMPLEX
what does the piriform cortex consist of
the primary olfactory area and primary auditory cortex
dedicated to olfaction - direct info from olfactory bulb
describe the different parts of the piriform cortex
aterior - produce representations of the chemical structure of the odour molecule
peripheral - produce representations of odour as a whole
describe the amgdalas role in olfaction
linked directly to olfactory bulb
activated by emotional stimuli - pleasant and unpleasant odours
sends signals to hypothallamus - invovled in instinctual behaviours ie hunger and smell of food
describe the entorhinal cortexs role in olfaction
passes info to the hippocampus
invovled in storage and retrieval of long term memories
link smell to previous experiences
describe the orbitofrontal cortexes role in olfaction
known as “secondary olfaction area”
recieveds info from amygdala, piriform cortex and entorhinal cortex
evaluates incoming stimuli as positive or negative
describe the representation of odour in the piriform cortex
seltler and axel 2009 - activation becomes more spread out compared to order in olfactory bulb as neural activation becomes associated
what types of taste sensations/tastants are there
sweet salty umami (savoury) bitter sour
what are tastants influenced by
onset/aftertaste
intensity
hedonics
loclisation
define onset/aftertaste
how the taste unfolds over time
define intensity of tastants
concentration of tastants
higher concentration = great receptivity of neurons
define hedonics of tastants
if the taste is pleasant or unpleasant
define the localisation of tastants
where the taste is sensed
what tastants are hedonically pleasant
sweet
salty
umami
mild sour
what tastants are hedonically unpleasant
strong sour
bitter
describe the structure of the tongue
back of tongue - circumvilitate and foliates
filliform in mid tongue
fungiform in end of tongue
describe a taste bud
within the filli and fungiform "fungiform papilla" has receptors on hair covered in tasre celles with taste pore similar to cilia connected to nerve fibres
describe tastant receptor sites
all sites specific to the tastant ie sour let in hydrogen, salt let in sodium
what types of papillae are there
fungiform
foliate
circumvilliate
filiform
- all contain tastebuds with certain taste cells that have receptors on the tip
define a GPCR receptor
release ATP into tissue fluid when activated
atp attach to cranial nerve presynaptic cells
ie sweet, bitter, umami
define a presynaptic receptor
passes info via serotonin to activate cranial nerve
ie salty, sour
what receptors and tastants pair for sweet
TR2 & TR3
what receptors and tastants pair for bitter
T2R1 & TR2
25-30 diff types as want to detect for toxicity
what receptors and tastants are tere for umami
T1R2 & T1R3
describe the connection between the mouth and the brain
faurion et al 1998
tongue>nucleas of salitary tracgt>thalamus>insula
insula>amygdala/orbitofrontal c/hypothallamus/anterior insula/frontal operalum/superior temp gyrus
how is the amygdala, orbitofrontal c and hypothallamus linked to taste
amygdala - representation of emotion
orbitofrontal c - reward value of food
hypothallamus - represent hunger
define flavour
the occurance which combines the taste in the mouth and the smell in the olfactory system
how does flavour occur
localisation of flavour occurs in mouth by oral capture - odour through retronasal path into mouth
how is flavour percieved in the nervous system
insula (taste) interacts with olfactory bulb, amygdala, orbitofrontal cortex and hypothallamus which are also involved in olfactory system
what other factors also contribute to the perception of flavour
hunger/thirst
expectation
vision
audition
how it feels in the mouth..ie. texture, temperature, spice, cool, dry etc
describe plassman et al 2008
marketing can influence the neural representation of experienced pleasantness
higher priced wine rated as increased pleasant and increased activity in orbitofrontal cortex
-same wine
describe o’doherty et al 2008
increased satiety of food can reduce pleasantness and make aversive
ie satiation in banana makes aversive
satiation in vanilla makes less pleasant
link between taste, olfaction and transduction
both molecules activate receptors in mouth and nose causing neural activity and therefore our percetion
